[PATCH] splice: only call wake_up_interruptible() when we really have to

__wake_up_common() is pretty heavy in the kernel profiles, this brings
it down to a more acceptable level.

Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 12 insertions, 4 deletions

diff --git a/fs/splice.c b/fs/splice.c
index 26f5f7ecee5c..9f796b1034d1 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -187,7 +187,9 @@ static ssize_t move_to_pipe(struct inode *inode, struct page **pages,
                 }
 
                 if (do_wakeup) {
-                        wake_up_interruptible_sync(PIPE_WAIT(*inode));
+                        smp_mb();
+                        if (waitqueue_active(PIPE_WAIT(*inode)))
+                                wake_up_interruptible_sync(PIPE_WAIT(*inode));
                         kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO,
                                     POLL_IN);
                         do_wakeup = 0;
@@ -201,7 +203,9 @@ static ssize_t move_to_pipe(struct inode *inode, struct page **pages,
         mutex_unlock(PIPE_MUTEX(*inode));
 
         if (do_wakeup) {
-                wake_up_interruptible(PIPE_WAIT(*inode));
+                smp_mb();
+                if (waitqueue_active(PIPE_WAIT(*inode)))
+                        wake_up_interruptible(PIPE_WAIT(*inode));
                 kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
         }
 
@@ -600,7 +604,9 @@ static ssize_t move_from_pipe(struct inode *inode, struct file *out,
                 }
 
                 if (do_wakeup) {
-                        wake_up_interruptible_sync(PIPE_WAIT(*inode));
+                        smp_mb();
+                        if (waitqueue_active(PIPE_WAIT(*inode)))
+                                wake_up_interruptible_sync(PIPE_WAIT(*inode));
                         kill_fasync(PIPE_FASYNC_WRITERS(*inode),SIGIO,POLL_OUT);
                         do_wakeup = 0;
                 }
@@ -611,7 +617,9 @@ static ssize_t move_from_pipe(struct inode *inode, struct file *out,
         mutex_unlock(PIPE_MUTEX(*inode));
 
         if (do_wakeup) {
-                wake_up_interruptible(PIPE_WAIT(*inode));
+                smp_mb();
+                if (waitqueue_active(PIPE_WAIT(*inode)))
+                        wake_up_interruptible(PIPE_WAIT(*inode));
                 kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
         }